Chemistry: fertilizers – Processes and products – Inorganic material
Reexamination Certificate
2000-05-24
2002-02-05
Sayala, Chhaya D. (Department: 1761)
Chemistry: fertilizers
Processes and products
Inorganic material
C071S036000, C071S059000
Reexamination Certificate
active
06344066
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for the combined production of (i) a fertilizer selected from a group consisting of ammonium nitrate, ammonium phosphate and a combination thereof through an indirect neutralization of ammonia with an acid selected from a group consisting of nitric acid, phosphoric acid and a combination thereof and of (ii) a sulfur compound selected from a group consisting of elemental sulfur, SO
2
, sulfuric acid and sulfate salts.
BACKGROUND ART
Fertilizers are used in large volumes of millions of tons per year. They are used all over the globe and throughout most of the year. Some of said fertilizers are salts produced by direct neutralization of an acid and a base. The main examples are ammonium nitrate, which is usually formed by the direct reaction of ammonia and nitric acid, and ammonium phosphates, usually formed in a reaction between phosphoric acid and ammonia. This direct reaction produces neutralization energy. The number of applications for said neutralization energy is limited.
Large amounts of sulfur are used, mainly for the production of sulfuric acid, which is used mainly as an acidulant in a variety of processes. In most cases it ends up as gypsum in landfills. A typical case is that of reacting phosphate rock with sulfuric acid to form phosphoric acid for agriculture applications and gypsum by-product which needs to be disposed of. Thus, sulfur consumption in such a process adds to the environmental problem by creating gypsum, but H
2
SO
4
is a cheap, concentrated and strong acid and therefore attractive for use. The problem could be reduced, if a good economic way was found for the recovery of sulfur compounds from flue gases thereby reducing the need to mine sulfur for use in phosphoric acid production.
Burning fossil fuel releases many millions of tons of SO
2
every year. Several processes were developed to absorb the SO
2
and convert it into sulfur or sulfuric acid. The industrial application of those technologies is very limited compared with other flue gas desulfurization processes. An important reason for that is the lack of a driving force for the separation and concentration of SO
2
out of flue gas. Adsorption of SO
2
and its release as such requires introduction of energy, usually thermal energy, which in turn consumes more fuel and adds to the problem.
The control of SO
2
emissions to the environment is one of the most urgent and critical problems being faced and addressed today. Annex IV to the 1994 Oslo Protocol on Further Reduction of Sulfur Emission lists general options for reduction of sulfur emissions from combustion: (i) Energy management measures including energy saving and energy mix, (ii) technological options including fuel switching, fuel cleaning, advanced combustion technologies, process and combustion modifications and flue gas desulfurization (FGD). The latter includes lime/limestone wet scrubbing (LWS), spray dryer absorption (SDA), Wellman Lord process (WL), ammonia scrubbing (AS) and combined NOx/SOx removal process (activated carbon (AC) and combined catalytic NOx/SOx removal). Two new processes, which have not passed (in 1994) the pilot stage, were listed: electron beam dry scrubbing (EBDS) and Mark 13A.
According to the Oslo Protocol, lime/limestone wet scrubbing (LWS) makes up 85% of all FGD installation. In 1995 the FGD sector accounted for 15% of all lime sales in the US, mostly through LWS. In the LWS process the acidic, gaseous SO
2
in the flue gas is adsorbed into a re-circulated water based slurry of gypsum+pretreated limestone, and is subsequently neutralized by reaction with the CaCO
3
. The products of the reaction are further reacted with air to produce predominantly calcium sulfate di-hydrate. The SO
2
removal capacity is dependent upon the inlet SO
2
content of the gas, the relative flow rate of the slurry and the pH of the slurry. In order to minimize the adverse impact of soluble compounds, introduced via the flue gas and the limestone, a stream is purged out the absorber. This purge stream is typically treated to precipitate and remove the soluble compounds in solid form prior to discharge.
LWS has many drawbacks associated with handling and recycling of solids, with the relatively low rate of reaction with the water immiscible base (CaCO
3
) and with the fact that a solid product is withdrawn from a recycling stream, which leads to build-up of soluble impurities. As reported by National Power of the U.K., the application of LWS in the 4,000 MW power unit at Drax, required an investment of about a billion USD, consumption of about 2% of the produced electric power for running the LWS unit and yearly operation costs of about $50 million.
Absorption in ammonia rather than in gypsum/lime slurry avoids many of the problems associated with the LWS process, but faces other problems. primarily associated with the cost of the ammonia. The ammonium sulfate formed in the reaction is a low-grade fertilizer, formed as a by-product of many other processes. Therefore, in most cases it does not cover the cost of ammonia.
A purpose of the present invention is to combine the production of (I) a fertilizer selected from a group consisting of ammonium nitrate and ammonium phosphates and of (II) a sulfur compound selected from a group consisting of elemental sulfur, SO
2
, sulfuric acid and sulfate salts.
Another purpose is to produce the fertilizer through indirect neutralization of ammonia with an acid selected from a group consisting of nitric acid, phosphoric add and a combination thereof.
Another purpose is to utilize the driving force associated with the production of the fertilizer, which is available in large amounts, in many locations and through most of the year, for the production of sulfur compounds from sulfur oxides containing gases.
Still another purpose of the present invention is to reduce air pollution caused by SO
2
.
DISCLOSURE OF THE INVENTION
With this state of the art in mind, there is now provided, according to the present invention, a method for the combined production of (I) a fertilizer selected from a group consisting of ammonium nitrate, ammonium phosphates or a combination thereof through an indirect neutralization of ammonia with an acid selected from a group consisting of nitric acid, phosphoric acid and a combination thereof and of (II) a sulfur compound selected from a group consisting of elemental sulfur, SO
2
, sulfuric acid and sulfate salts, said method comprising:
(a) contacting a sulfur oxide containing gas, resulting from the combustion of sulfur-containing hydrocarbons, and containing carbon dioxide in concentrations greater than that of the sulfur oxide in said gas with ammonia and an aqueous liquor, whereby a sulfur oxide containing product is selectively formed and the resulting gas has a reduced SO
2
content;
(b) reacting a sulfur oxide containing product resulting from step (a) with a reagent selected from a group consisting of nitric acid, phosphoric acid, a mixture thereof and salts formed by the reaction of said acids to form said fertilizer and a sulfur compound, and
(c) separating at least a portion of said sulfur compound from said fertilizer.
The sulfur oxide in the gas used in step (a) is in most case SO
2
, SO
3
and a mixture thereof. For simplicity of presentation it will be referred to in the following as SO
2
. The sulfur oxide containing gas could result from various industrial productions involving the combustion of sulfur-containing hydrocarbons but of be highest interest is the case of flue gas from combustion of oil and coal. Of a particularly high interest are those cases where high sulfur fuel is used. In a preferred embodiment the sulfur oxide containing gas is a product of an FGD process, more preferably FGD via the LWS. In a most preferable embodiment the flue gas is treated, by LWS or another FGD process, for the removal of less than 90% of the SO
2
content, more preferably less than 80%, and the resulting gas is treated according to the method of the present invention.
In U.S. Pat. No. 3,421,848 ther
Clue
Sayala Chhaya D.
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